Iron complexes corrins

The iron porphyrins and related compounds constitute an extremely important class of coordination complex due to their chemical behaviour and involvement in a number of vital biological systems. Over recent years a vast amount of work on them has been published. Chapter 21.1 deals with the general coordination chemistry of metal porphyrins, hydroporphyrins, azaporphyrins, phthalocyanines, corroles, and corrins. Low oxidation state iron porphyrin complexes are discussed in Section 44.1.4.5 and those containing nitric oxide in Section 44.1.4.7, while a later section in this chapter (44.2.9.2) is mainly concerned with iron(III) and higher oxidation state porphyrin complexes. Inevitably however, a considerable amount of information on iron(II) complexes is contained in that section as well as in Chapter 21.1. Therefore in order to prevent excessive duplication, the present section is restricted to highlighting some of the more important aspects of the coordination chemistry of the iron(II) porphyrins while the related unusually stable phthalocyanine complexes are discussed in the previous section. 

As we will see in subsequent chapters, many metalloproteins have their metal centres located in organic cofactors, like the tetrapyrrole porphyrins and corrins, in metal clusters like the Fe—S clusters in iron—sulfur proteins, or in even more complex cofactors, like the FeMo-cofactor of nitrogenase. We discuss their structures briefly here before moving on in a selected number of cases to the way in which metal insertion into the cofactor is engineered. 

The rapidity of substitution reactions at a metal surrounded by a porphyrin or corrin group seems to be connected with r-delocalization and a strong in-plane ligand field which is not present in normal complexes. The substitution reactions (4) of five-co-ordinate neutral dithiolen complexes (where M is iron or cobalt and L and [M(S2CaPh2)2X] + L—> [M(S2C2Ph2)2L] + X (4)... 

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